Long-term care residents and staff should be top candidates for a COVID-19 vaccine booster if and when these shots are needed, say expert advisers to the Centers for Disease Control and Prevention.

The Advisory Committee on Immunization Practices, or ACIP, met Wednesday, June 23, to consider factors that might be a reasonable prompt for recommending boosters. Group members, who independently advise the CDC, concluded that the data do not yet support the need for a broad U.S. booster shot campaign. Existing vaccines are currently able to counteract the dominant coronavirus variants in the United States, they said.

But a rise in new infections or breakthrough infections in vaccinated groups may be a future signal that these additional shots are needed, they said. 

For long-term care residents, the high effectiveness of initial COVID-19 vaccinations is encouraging, ACIP said. Residents were vaccinated relatively early in the campaign, however, and time from vaccination plays into waning effectiveness, the group added. What’s more, this population already requires special considerations for other vaccines, including the use of boosters and higher-dose vaccines (as in influenza shots) to increase effectiveness, they said. 

Healthcare personnel, for their part, also often were vaccinated early in the vaccine rollout and are subject to repeated potential exposure to the COVID-19, “even as rates of community transmission improve,” the committee noted.

The CDC advisers weighed four key risk factors in their conclusions: COVID-19 complications, exposure, waning immunity and COVID-19 gene variants. The initial effectiveness of a vaccines may help to predict the time until vaccine boosting is needed, they noted. A shot with initial efficacy of 95% is expected to maintain 77% efficacy after 250 days, for example, whereas a shot with initial efficacy of 70% will be only 33% effective after the same time period, they reported.

WHO forecasts annual shots for seniors

The World Health Organization, meanwhile, predicts that annual vaccine boosters may be needed for those most vulnerable to COVID-19, such as the elderly, according to an internal document obtained by Reuters.

The WHO “considers annual boosters for high-risk individuals as its ‘indicative’ baseline scenario, and boosters every two years for the general population,” the news outlet reported last week.

More than 87% of U.S. adults aged 65 and older have had at least one COVID-19 vaccine dose so far, ACIP noted.